The configurational thermodynamic properties of fcc-based Al-Sc alloys and coherent ${\mathrm{A}\mathrm{l}/\mathrm{A}\mathrm{l}}_3\mathrm{Sc}$ interphase-boundary interfaces have been calculated from first principles. The computational approach used in this study combines the results of pseudopotential total-energy calculations with a cluster-expansion description of the alloy energetics. Bulk and interface configurational-thermodynamic properties are computed using a low-temperature-expansion technique. Calculated values of the {100} and {111} ${\mathrm{A}\mathrm{l}/\mathrm{A}\mathrm{l}}_3\mathrm{Sc}$ interfacial energies at zero temperature are, respectively, 192 and $226{\mathrm{m}\mathrm{J}/\mathrm{m}}^2.$ The temperature dependence of the calculated interfacial free energies is found to be very weak for {100} and more appreciable for {111} orientations; the primary effect of configurational disordering at finite temperature is to reduce the degree of crystallographic anisotropy associated with calculated interfacial free energies. The first-principles-computed solid-solubility limits for Sc in bulk fcc Al are found to be underestimated significantly in comparison with experimental measurements. It is argued that this discrepancy can be largely attributed to nonconfigurational contributions to the entropy which have been neglected in the present thermodynamic calculations.

• Received 17 November 1997

DOI:https://doi.org/10.1103/PhysRevB.57.11265